Iceberg Grounding on Seafloor (Slow Down)

This sound was recorded May 19, 1997 on the eastern equatorial Pacific Ocean autonomous hydrophone array. The origin time and source location are 15:30 GMT near 62°S, 60°W. This is an area off the Antarctic Peninsula with numerous islands and shoals and it is highly probable that this sound was produced by a large iceberg as it became grounded. The sound slowly descends in frequency over about 7 minutes as the drifting iceberg slows to a stop once it comes in contact with the seafloor, however it was of sufficient amplitude to be heard on three sensors at 110W, and 8S, 0, and 8N, at a range of nearly 5,000 km. The South American continent blocked the great circle path from this location to the three eastern sensors located along the 95° longitude line. This type of signal has been recorded numerous times as large icebergs run aground (MacAyeal et al., 2008). Often, after a “slowdown” occurs, a “speedup” follows an aseismic eye of no seismicity associated with local slack tide. This has been interpreted to reflect the acoustic energy of the grounded iceberg responding to the changing tides.